The invention relates to a spring clutch which uses a spring to wrap onto a first member, thereby transferring torque between the first member and a second member. More particularly, the invention relates to the use of torque slip clips to provide an interface between the spring and the second member.
Many variations of spring clutches have been developed and are familiar to those skilled in the art. A typical spring clutch has (1) an input member to which an external source of motive force is connected, (2) an output member from which, when the clutch is engaged, torque can be transmitted to the connected load, (3) a spring which is used to connect the input and the output members, and (4) a control element by means of which the clutch is engaged or disengaged. Such a clutch is commonly called a wrap spring clutch because a spring is controllably wrapped either around or within the input or the output member. When the spring is caused to grip that member, the clutch can transmit torque and is said to be engaged. Conversely, when the spring is caused to be released from that member, the clutch will not transmit more than a small, residual amount of torque and is said to be disengaged. The control element is used to control the action of the spring, causing it to form the mechanical connection between the driving and the driven members when the clutch is engaged, and causing that connection to be substantially interrupted when the clutch is to be disengaged. The spring is either normally engaged or normally disengaged and the control element can be used to change the spring from the normal condition to the actuated condition.
One problem with the use of spring clutches is that in an application where a quick response is required between the engagement of the input member to the output member, a significant xe2x80x9cline shockxe2x80x9d (large amounts of force delivered to the spring in a very short time) can occur through the spring. Line shock increases as the inertia load on the output member is increased and/or as the response time (the time which it takes for the output member to be brought up to speed by the input member) is shortened since both of these require a high initial torque applied to the spring to rotate the output member. The result is that high levels of wear are generated by the frictional interference of the spring, high audible noise levels are generated by the clutch as it engages, and high levels of stress are imposed on the spring. In the past, to solve these problems, the size of the clutch was increased by utilizing large springs and wear inserts as load levels were increased.
Another problem associated with the use of spring clutches is their vulnerability to damage from overloading. Clutches are usually rated by the amount of torque which they are capable of transmitting. Most spring clutches are designed to be used only in situations in which the rated torque will not be exceeded. Spring clutches are usually damaged if the rated torque is exceeded by more than the safety margin designed into the clutch. Previous overload protection devices for spring clutches would not precisely actuate at an overload level. Additionally, previous overload protection devices were not available for applications requiring high torque levels. Thus, since dependable overload protection was not available, the capability of a spring clutch to withstand overload conditions depended upon a number of factors, including the physical size of the clutch. Specifically, by increasing the size and stiffness of the spring wire, the diameter of the element to which the spring makes a frictional connection when the clutch is engaged, and the size of the spring when it is in its relaxed condition, the clutch was able to withstand spikes of torque. Understandably, as the size of the elements of the clutch are increased the entire clutch got bigger.
Unfortunately, in many of the applications where it is desirable to use a spring clutch, physical space is at a premium. Therefore, there is a need in the art for providing a spring clutch capable of transferring high torque with a quick response and providing precise overload protection having the ability to actuate at higher torque levels which allows the use of a physically smaller clutch.
The invention is a spring clutch mechanism including a first member and a second member coaxially disposed with respect to the first member where at least one of the first and second members is rotatable. A wrap spring assembly is in rotational engagement with the first member. At least one slip clip, which has an outer axially extending surface and an axially extending aperture which forms an inner axially extending surface, is disposed in rotational engagement between the second member and the wrap spring assembly.